1. Field of the Invention
The present invention relates generally to an organic electroluminescent apparatus having a plurality of organic electroluminescent devices each having an organic layer having luminescent properties provided between a hole injection electrode and an electron injection electrode in a separated state and a method of fabricating the same, which is characterized in that the plurality organic electroluminescent devices each having the organic layer having luminescent properties provided between the hole injection electrode and the electron injection electrode are simply and suitably arranged in a separated state, and particularly the plurality of organic electroluminescent devices can be suitably separated from each other even when the organic layer having luminescent properties contains a macromolecular material.
2. Description of the Related Art
In recent years, the needs of flat panel display devices the consumed power and the size of which are smaller than those of a CRT (cathode-ray Tube) which has been heretofore generally employed have been increased as information equipments are diversified, for example. An electroluminescent device has been paid attention to as one of the flat panel display devices.
The electroluminescent device is roughly divided into an inorganic electroluminescent device and an organic electroluminescent device depending on a used material.
The inorganic electroluminescent device is so adapted that a high electric field is generally exerted on a luminance portion, and electrons are accelerated within the high electric field to collide with a luminescence center, whereby the luminescence center is excited to emit light.
On the other hand, the organic electroluminescent device is so adapted that electrons and holes are respectively injected into a luminescent portion from an electron injection electrode and a hole injection electrode, the electrons and the holes thus injected are recombined with each other in a luminescence center to bring an organic molecule into its excited state, and the organic molecule emits fluorescence when it is returned from the excited state to its ground state.
In the case of the inorganic electroluminescent device, a high voltage of 100 to 200 volts is required as its driving voltage because a high electric field is exerted as described above. On the other hand, the organic electroluminescent derive can be driven at a low voltage of approximately 5 to 20 volts.
In the case of the organic electroluminescent device, a light emitting device emitting light in a suitable color can be obtained by selecting a fluorescent material that is a luminescent material. It is expected that the organic electroluminescent device can be also utilized as a multi-color or full-color display device, for example.
In recent years, fabricated as an organic electroluminescent apparatus such as an organic electroluminescent panel has been one having a plurality of organic electroluminescent devices, described above, arranged thereon in a separated state.
Conventionally in fabricating the organic electroluminescent apparatus having the plurality of organic electroluminescent devices arranged thereon in a separated state, a hole injection electrode has been generally formed in a predetermined pattern on a transparent substrate such as a glass substrate and separated, and an organic layer and an electron injection electrode which are formed on the hole injection electrode have been also respectively formed in predetermined patterns and separated.
Although an operation for forming the hole injection electrode formed in a predetermined pattern on the transparent substrate and separating it, as described above, particularly presents no problem, an operation for respectively forming the organic layer and the electron injection electrode in predetermined patterns on the hole injection electrode and separating them presents a problem.
Specifically, the organic layer used for the organic electroluminescent device is generally low in heat resistance, solvent resistance, and humidity resistance. When the organic layer and the electron injection electrode formed on the organic layer are formed in predetermined patterns by photolithography or the like, there are some problems. For example, a solvent in photoresist enters the organic layer, the organic layer is dissolved in an etchant, and an organic layer is damaged by plasma at the time of dry etching.
Therefore, the organic layer and the electron injection electrode have been heretofore generally formed in predetermined patterns by evaporation using a mask member. When they are thus evaporated using the mask member, however, fine processing cannot be performed.
In recent years, an organic electroluminescent apparatus so adapted that a hole injection electrode is formed in a suitable pattern on a transparent substrate, a barrier having electrical insulating properties with a suitable pattern is provided on the transparent substrate, an organic layer and an electron injection electrode are successively laminated by evaporation from above the barrier, and the organic layer and the electron injection electrode are respectively separated by the barrier has been proposed, as disclosed in JP-A-8-227276, JP-A-8-315981, JP-A-9-102393, etc.
In JP-A-8-315981 and JP-A-9-102393, in providing a patterned barrier 3 on a hole injection electrode 2 formed on a transparent substrate 1, an upper surface 3a of the barrier 3 is increased in size to provide an overhang portion, as shown in FIG. 1.
When an organic layer 4 is evaporated from above the barrier 3 having the overhang portion thus provided by increasing the size of the upper surface 3a, the organic layer 4 is not formed under the overhang portion, so that an exposed part of the hole injection electrode 2 remains under the overhang portion. When the electron injection electrode 5 is then evaporated, the electron injection electrode 5 may be short-circuited upon being formed on not only the organic layer 4 but also the exposed part of the hole injection electrode 2.
In recent years, an organic layer having luminescent properties using a macromolecular material that is high in heat stability and is superior in durability has been paid attention to.
The organic layer containing the macromolecular material can be generally formed simply by dipping or spin coating. When the patterned barrier 3 is provided on the hole injection electrode 2 formed on the transparent substrate 1 as described above, however, the barrier 3 interferes with the formation. Therefore, it is difficult to form the organic layer 4 using the macromolecular material by the above-mentioned method.
In the case of the above-mentioned organic layer containing the macromolecular material, erosion by an etchant or the like is restrained. Consequently, it is considered that an electron injection electrode is provided on the organic layer containing the macromolecular material, and the electron injection electrode is formed in a predetermined pattern by photolithography or the like.
When the electron injection electrode is formed in a predetermined pattern by photolithography or the like, however, it is difficult to control etching because the thickness of the electron injection electrode is generally small. Therefore, the etchant penetrates into a portion between the organic layer containing the macromolecular material and the electron injection electrode, so that some problems occur. For example, contact characteristics between the organic layer and the electron injection electrode are degraded. When an electrode material having a small work function such as magnesium is used as a material composing the electron injection electrode such that electrons are efficiently injected into the organic layer from the electron injection electrode, some problems occur. For example, the electron injection electrode is degraded upon being oxidized by water or the like of the etchant, so that light cannot be stably emitted.
An object of the present invention is to make it possible to arrange, in an organic electroluminescent apparatus in which a plurality of organic electroluminescent devices each having an organic layer having luminescent properties provided between a hole injection electrode and an electron injection electrode are arranged with they being separated from one another, the electroluminescent devices in a separated state simply and suitably.
Another object of the present invention is to make it possible to simply form, when an organic layer having luminescent properties contains a macromolecular material, the organic layer containing the macromolecular material using dipping or spin coating as well as make it possible to arrange organic electroluminescent devices in a separated state simply and suitably.
In an organic electroluminescent apparatus according to the present invention, in arranging a plurality of organic electroluminescent devices each having an organic layer having luminescent properties provided between a first electrode and a second electrode in a separated state, a barrier having electrical insulating properties is formed in a predetermined pattern on the organic layer, to separate the organic electroluminescent devices from each other by the barrier.
An example of such an organic electroluminescent apparatus is one comprising a first electrode formed in a predetermined pattern on a substrate, an organic layer having luminescent properties provided on the first electrode, a barrier having electrical insulating properties formed in a predetermined pattern on the organic layer, and a second electrode formed on the organic layer upon being separated by the barrier having electrical insulating properties.
A method of fabricating an organic electroluminescent apparatus according to the present invention comprises the steps of providing a first electrode in a predetermined pattern on a substrate, providing an organic layer having luminescent properties on the first electrode, providing a barrier having electrical insulating properties with a predetermined pattern on the organic layer, and providing a second electrode separated by the barrier having electrical insulating properties on the organic layer.
In the method of fabricating the organic electroluminescent apparatus according to the present invention, the first electrode with a predetermined pattern is formed on the substrate, the organic layer having luminescent properties is provided on the substrate having the first electrode formed thereon, the barrier having electrical insulating properties with a predetermined pattern is provided on the organic layer, and the electron injection electrode is provided from above the barrier having electrical insulating properties. Consequently, the electron injection electrode is separated by the barrier, so that the organic electroluminescent devices are arranged in a separated state.
In the present invention, the barrier having electrical insulating properties is provided on the organic layer. Even when the upper surface of the barrier is increased in size to provide an overhang portion, the first electrode is not exposed under the overhang portion. When the second electrode is formed, the second electrode and the first electrode are not short-circuited upon being brought into contact with each other.
In the present invention, the organic layer is formed, and the barrier is then provided on the organic layer. When the organic layer is formed by painting the substrate having the first electrode formed thereon with a macromolecular material solution by the method of dipping or spin coating, therefore, the barrier does not interfere with the formation.
Examples of the macromolecular material used for the organic layer include macromolecular materials having fluorescent properties such as a poly(p-phenylene vinylene) derivative, polythiophene, and polyvinyl carbazole, and macromolecular materials having electrical insulating properties, in which a pigment is doped, such as polymethyl methacrylate and polycarbonate.
In providing the barrier having electrically insulating properties on the organic layer, when a macromolecular material solution for barrier formation is applied, the applied macromolecular material solution for barrier formation is solidified, and the barrier having electrically insulating properties with a predetermined pattern is then formed by etching, used as the macromolecular material in the organic layer is one which is insoluble in the macromolecular material solution for barrier formation or an etchant.
Furthermore, in the present invention, when the barrier having electrical insulation properties with a predetermined pattern is provided on the organic layer, and an electrode material is evaporated from above the barrier having electrical insulating properties, to provide a second electrode on the organic layer separated by the barrier having electrical insulating properties, the second electrode formed on the organic layer need not be formed in a predetermined pattern upon being processed by an etchant. Therefore, the possibilities that the etchant penetrates into a portion between the organic layer and the second electrode as in the conventional example, so that contact properties between the organic layer and the second electrode are degraded, and the second electrode is degraded upon being oxidized are eliminated, so that light can be stably emitted in each of the organic electroluminescent devices.
There and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiment of the invention.